The present invention relates to multi-layer magnetic films, and more particularly relates to a ferromagnetic film deposited on a film comprising iridium, manganese and nitrogen (IrMnN). The IrMnN film may act as a seed layer and/or exchange biasing layer for the ferromagnetic film. The films are useful in applications such as read sensors for magnetic recording heads and soft magnetic underlayers for perpendicular magnetic recording media.
Magnetic films are used in magnetic sensors, such as magnetoresistance (MR) and giant magnetoresistance sensors (GMR). For example, devices utilizing GMR effects have utility as read heads used in magnetic disc storage systems. GMR sensors typically comprise a stack of thin sheets of a ferromagnetic alloy, such as NiFe (Permalloy), magnetized along an axis of low coercivity. The sheets are usually mounted in the head so that their magnetic axes are transverse to the direction of disc rotation and parallel to the plane of the disc. The magnetic flux from the disc causes rotation of the magnetization vector in at least one of the sheets, which in turn causes a change in resistivity of the stack. In operation, a sense current is passed through a GMR stack. The presence of magnetic field in the storage media adjacent to the sensor changes the resistance of a GMR stack. A resulting change in voltage drop across the GMR stack due to the change of the resistance of the GMR stack can be measured and used to recover magnetically stored information.
Magnetic sensors utilizing the GMR effect are frequently referred to as spin valve sensors. A spin valve sensor is typically a sandwiched structure including two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the pinned layer because it is magnetically pinned or oriented in a fixed and unchanging direction. A common method of maintaining the magnetic orientation of the pinned layer is through antiferromagnetic exchange coupling utilizing an adjacent or nearby antiferromagnetic layer, commonly referred to as the pinning layer. The other ferromagnetic layer is called the free or unpinned layer because its magnetization can rotate in response to the presence of external magnetic fields.
The output voltage is affected by various characteristics of the sensor. The sense current can flow through the stack in a direction that is perpendicular to the planes of the stack strips, i.e., current-perpendicular-to-plane or CPP, or the sense current can flow through the stack in a direction that is parallel to the planes of the stack strips, i.e. current-in-plane or CIP. The CPP operating mode can result in higher output voltage than the CIP operating mode. Higher output voltages permit greater precision and sensitivity of the read sensor in sensing magnetic fields from the magnetic medium.
The benefits of spin valve sensors result from a large difference in electrical conductivity exhibited by the devices depending on the relative alignment between the magnetizations of the GMR element ferromagnetic layers. In order for antiferromagnetically pinned spin valve sensors to function effectively, a sufficient pinning field from the pinning layer is required to keep the magnetization of the pinned ferromagnetic layer unchanged during operation. Various antiferromagnetic materials, such as NiMn, FeMn, NiO, IrMn, PtPdMn, CrMnPt, RuRhMn and TbCo, have been used or proposed as antiferromagnetic pinning layers for spin valve sensors. For example, Ir20Mn80 films deposited by sputtering in an inert atmosphere exhibit an exchange coupling effect, but require an additional (111) textured ferromagnetic film, e.g. Ni80Fe20, as a seed layer below the deposited IrMn film in order to produce the effect.
In addition to their use in GMR sensors, multi-layer magnetic films may be used in perpendicular magnetic recording media. Conventional perpendicular recording media typically include a hard magnetic recording layer and a soft magnetic underlayer which provides a flux path from a trailing write pole to a leading opposing pole of the writer. To write to the magnetic recording media, the recording head is separated from the magnetic recording media by a distance known as the flying height. The magnetic recording media is moved past the recording head so that the recording head follows the tracks of the magnetic recording media. Current is passed through the coil to create magnetic flux within the write pole. The magnetic flux passes from the write pole tip, through the hard magnetic recording track, into the soft underlayer, and across to the opposing pole. The soft underlayer also helps during the read operation. During the read back process, the soft underlayer produces the image of magnetic charges in the magnetically hard layer, effectively increasing the magnetic flux coming from the medium. This provides a higher playback signal.
One of the challenges of implementing perpendicular recording is to resolve the problem of soft underlayer noise. The noise may be caused by fringing fields generated by magnetic domains, or uncompensated magnetic charges, in the soft underlayer that can be sensed by the reader. If the magnetic domain distribution of such materials is not carefully controlled, very large fringing fields can introduce substantial amounts of noise in the read element. Not only can the reader sense the steady state distribution of magnetization in the soft underlayer, but it can also affect the distribution of magnetization in the soft underlayer, thus generating time dependent noise. Both types of noise should be minimized.
In addition, the soft underlayer may form stripe domains, which generate noticeable noise and considerably reduce the signal-to-noise ratio of the recording medium. These stripe domains in the soft underlayer can be suppressed by applying an in-plane bias field. The bias field increases the effective anisotropy field of the soft underlayer and prevents domain formation that results in a permeability decrease. Techniques such as antiferromagnetic exchange biasing may be used to form the in-plane bias field. The antiferromagnetic exchange technique utilizes an antiferromagnetic film that is placed in direct contact with the ferromagnetic soft layer and forms antiferromagnetic exchange coupling between the layers. However, conventional antiferromagnetic materials have low corrosion resistance and require high temperature annealing to form exchange coupling. Furthermore, conventional antiferromagnetic materials have low blocking temperatures which limit their use in applications subject to elevated temperatures.
The present invention has been developed in view of the foregoing.
The present invention provides films comprising iridium, manganese and nitrogen (IrMnN). In accordance with an embodiment of the present invention, ferromagnetic thin films may be deposited on the antiferromagnetic IrMnN film. The IrMnN film may be made by reactively sputtering IrMn in a reactive nitrogen-containing atmosphere. The IrMnN film has a (200) growth texture. As used herein, the phrase xe2x80x9c(200) texturexe2x80x9d refers to the tendency for the film to grow with its crystals predominantly square with the film surface, e.g., the cube faces are either parallel or orthogonal to the film surface. For example, the (200) texture may comprise (100) crystallographic lattice planes of a face-centered cubic structure which lie parallel with the film surface. The IrMnN antiferromagnetic film differs from prior systems by providing an exchange coupling mechanism without requiring a (111) seed layer and/or a (111) orientation of the antiferromagnetic IrMn layer. The actual exchange bias effect and blocking temperature achieved by the IrMnN film are larger than for the pure IrMn film, making the present IrMnN antiferromagnetic films advantageous for use in perpendicular media as well as other applications.
An aspect of the present invention is to provide a film comprising IrMnN having a (200) texture.
Another aspect of the present invention is to provide a layered magnetic structure comprising an IrMnN layer, and a ferromagnetic layer deposited on the IrMnN layer.
A further aspect of the present invention is to provide a method of making an IrMnN film comprising depositing Ir and Mn on a substrate in the presence of a reactive nitrogen-containing atmosphere.
Another aspect of the present invention is to provide a method of making an IrMnN film comprising depositing the IrMnN film on a substrate, wherein the IrMnN film has a (200) texture.
A further aspect of the present invention is to provide a method of making a layered magnetic structure comprising providing an IrMnN layer, and depositing a ferromagnetic layer on the IrMnN layer.
These and other aspects of the present invention will be more apparent from the following description.